A “radio detection and ranging” (RADAR or radar) system is often used to detect, range, and map objects. In operation, strong radio waves are transmitted, and then a receiver listens for the reflected echoes and measures their Doppler shifts. There have been many different uses discovered for such radar systems.
One recent use involves the employment of radar techniques to detect minute body movements, which are associated with respiratory activity. This approach is based on the principle that breathing produces measurable phase changes in electromagnetic waves as they reflect off of a living subject. Motion detection is achieved by transmitting an interrogating electromagnetic field at the target of interest, and then measuring the time-delay of the return signal reflected back from the surface of the target. When a target surface is moving, as does the surface of a chest of a living subject in conjunction with respiratory and cardiac activities, corresponding variations will be observed in the measured time-delay. The observed variations can be used to determine motion-related target parameters such as displacement and velocity.
From this line of research and development, a device has been developed called a “radar flashlight.” The radar flashlight is designed to detect the respiration of a living subject behind a wall, door or an enclosed space with non-conductive walls. The unit also has application to the location of conscious or unconscious persons in a smoke filled or chemical contaminated office building.
When a radar detection device, such as the radar flashlight, is not stabilized, the user's hand motion is transferred to the wall and other non-moving objects illuminated by the radar. When the radar detection device is in motion, it receives Doppler shifted signals that are generated from its own motion referenced to fixed objects in front of the receiver. This produces radar clutter, which refers to any objects that cause unwanted reflections of a radar's electromagnetic energy to be returned to the radar receiver. The unwanted returns compete with valid returns of interest and cause the radar receiver and radar displays to become cluttered and more difficult to decipher. Depending on the radar cross section of the radar clutter, the clutter return can be very large compared to the small return from the chest motion generated by respiration. The result is that a moving or breathing body cannot be distinguished from a stationary target of a living subject on the other side of an intervening wall.
Thus, a heretofore unaddressed need exists in the industry to address the aforementioned deficiencies and inadequacies.